Clear cache of pages is now handle by PageManager

Clear cache logic is now in Page class, we didn't care wich attributes we have to alter in the page to clear the cache
 #122: Add website clear cache button
fix modifications typo inside translation files
remove clearCache logic form clearCacheAction

Logic has been moved to PageManager inside clearCacheFromWebsite
add useful comment to explain how cache are cleared in the page
if something went wrong during cache clear we only show to the user the default flash message
move inline comment to phpdoc comment
Merge pull request #132 from BenoitLeveque/clear-website-cache

Add a clear website cache on website admin page